Segmental resection is a basic component of the surgical treatment of malignant mandibular tumors. Incidence of oral cancer in the US is 7.7/100,000 (30,000 case/year). Surgical resection may be followed by radiotherapy or chemotherapy. Definitive treatment of many of the more common benign tumors may also require segmental resection due to high incidence of local recurrence after simple curettage or intra-lesional excision. These tumors include ameloblastoma, myxoma, giant cell granuloma and recurrent keratocyst. Blast injuries and high impact trauma to the mandible may lead to segmental bone loss either directly or due to surgical debridement. Segmental bone loss may also result from repeated surgical debridement for treatment of chronic osteomyelitis of the mandible.
All these conditions require reconstruction of the lower jaw, including the bone, the gingiva and the teeth. After resection of malignant tumors, more soft tissue reconstruction is often necessary. This may include the floor of the mouth, the tongue, the cheek, the chin, in addition to adequate soft tissue covering of the major vessels of the neck following neck dissection. This has always been a challenging task. In spite of the wide variety of reconstruction methods, none of them is completely satisfactory.
The general aim of oral reconstruction is to restore both the normal physiology and the facial aesthetics. Physiological functions include the maxillo-mandibular occlusion, mastication (jaw dynamics), deglutition, mandibular continuity, sensibility of the mucosa, sufficient alveolar ridge height and thickness, lip competence and speech. Aesthetic goals include the general appearance of the reconstructed soft-tissue, facial symmetry, restoration of dentition, and preservation of the lower facial dimensions.
The principle current reconstruction methods include mandibular reconstruction plate with or without bone grafting. A traditional mandibular reconstruction plate is a rigid titanium bone plate that connects the remaining bone stumps after segmental excision. The maxillo-mandibular central occlusion has to be achieved first by intermaxillary wire fixation. The plate prevents displacement of bone segments, soft-tissue collapse, and preserves facial symmetry. Soft-tissue reconstruction is then carried out to provide the proper covering and lining of the plate. This is usually the first of two reconstruction steps. The second step, definitive bone reconstruction, is often delayed to allow for radiotherapy to take place, eliminate the possibility for local recurrence or simply not to add to the longevity of the first operation. However, some surgeons prefer to do primary bone reconstruction at the same setting provided that no radiotherapy is needed and no recurrence is anticipated. Others, however, prefer not to do the definitive bony reconstruction at all. Although good aesthetic results were reported with reconstruction plate alone with no bone replacement, this deprives the patient of having any restoration of occlusion, not even a removable lower denture.
During the second stage of reconstruction, the gap is explored, and the whole width of the tumor bed as well as the edges of the remaining bone is dissected. This step is often technically difficult due to extensive fibrosis, loss of anatomical planes and landmarks, and the possibility of vascular injury that can result in serious bleeding or injury to the oral mucosa. Communication with the oral cavity due to mucosal breaks during dissection has a high chance of resistant postoperative infection. After complete dissection, the plate is removed and the bone graft (either vascularized or non-vascularized) is inserted in its place. The procedure is lengthy and highly demanding especially when microvascular techniques are used. The overall outcome of this technique, with either primary or secondary bone reconstruction was less than satisfactory. Failure rate of metal plate with bone graft was between 16–29%, while complication rate varied from 45–81%. Some factors were found to be more related to graft failure, the most important of which are the amount of intra-operative blood loss and the occurrence of recipient site complications (e.g. fistula and infection).
Disadvantages of free non-vascularized bone graft include graft resorption, high incidence of failure due to resistant infection, especially with primary reconstruction, insufficient amount of bone for large gaps and donor site morbidity. Except for iliac crest graft, the harvested bone mass was not sufficient either for osseointegrated implant insertion or carrying a removable lower denture. Disadvantages of free vascularized bone graft (free flaps) are discussed in the next section.
A substitute for the reconstruction plate has been a titanium mesh, which is shaped according to the gap after tumor excision, and then it is filled with bone graft either immediately or at a later stage. Although the mesh does have to be removed after reconstruction, it still requires the use of large amount of autogenous bone graft, and has a high failure rate mainly due to resistant infection necessitating removal of the prosthesis. Again, rehabilitation of jaw function was not achieved by this method. The tendency towards definitive reconstruction of bone as a part of the primary surgery is growing over the years. However, achieving acceptable results with primary reconstruction methods was never an easy task.
The use of non-vascularized bone graft during primary reconstruction is not advised due to high incidence of failure. The description of microvascular techniques in the early seventies provided more options for primary reconstruction of the mandible. Over the years, many designs for vascularized osseomyocutanous flaps for mandibular reconstruction were reported; the most popular of which are the vascularized fibula, scapula and iliac crest. They had better functional results, with the possibility to carry tooth restorations for full mouth rehabilitation, and the ability to reconstruct large and composite defects, even in growing patients.
In spite of their promising success rate, free vascularized flaps have high rates of complications, especially medical complications, which may be as severe as postoperative death. These highly demanding techniques, which require a specialized surgical team, definitely add to the longevity and complications of the primary surgery. In an average procedure of tumor resection with free fibular graft mandibular reconstruction, two surgical teams are operating simultaneously for more than 10 hours. Considering the general condition of the cancer patient, reconstructive surgery should be as brief and less invasive as possible.
Other disadvantages of vascularized tissue transfer include donor site morbidity. Leg pain, ankle instability have been reported with the vascularized fibula; herneas, hip pain, and anesthesia of the lateral thigh with vascularized iliac crest; and limitation of shoulder range of motion with vascularized scapula. Additionally, the characteristics of each flap design limited its use to only specific defects.
Distraction Osteogenesis in Mandibular Reconstruction
Distraction osteogenesis is a process of new bone formation between two bone segments, when they are gradually separated by incremental traction. This pattern of bone elongation allows the surrounding soft tissues to adjust to the new skeletal dimensions through the series of adaptive changes called distraction histiogenesis. Active histiogenesis has been shown to occur in various soft tissues including skeletal muscles, nerves, blood vessels, periodontal ligament, and gingiva. The result will be the synthesis of new bone with a cover of periostium and soft tissues (mucosa, muscles, etc.) as well as new vascular and nerve supply.
Using this technique, bone defects in long bones could be reconstructed without bone grafting, but by surgically separating a bone segment (transport disc) from one, or both edges of the remaining bone and gradually distracting this segment in the direction of the opposite bone edge. New bone will develop behind the distracted segment filling the gap until it reaches the docking site. Recent results of mandibular reconstruction using this principle were very promising. Newly formed bone proved to have normal architecture (inner cortex, outer cortex, and medulla), dimensions, and 80–100% of normal mechanical properties when examined after 8 weeks of consolidation.
Distraction devices designed for reconstruction of mandibular bone defects had two forms. The first is a uni-or-multidirectional distraction device mounted on, or combined with reconstruction plate. The second is an extra-oral titanium arch with movable units anchored to mandibular bone segments through steel pins.
Distraction Devices Mounted on or Combined with Reconstruction Plate
Each of these devices is composed of a distraction device, which is either mounted on (connected to) the plate, or totally separate from it. The distraction device can be uni-directional or multi-vector; extra-oral or intra-oral. However, in addition to the technical problems associated with device assembly and application, the distraction devices had a completely independent function to the reconstruction plate. While the reconstruction plate takes the curved shape of the original mandible, the distraction device carries the transport segment towards the docking site guided by the linear vector of the distraction device irrelevant to the course of the reconstruction plate. In other words, the fixative function of the reconstruction plate was separated from the new bone formation, even when the two device components were physically connected. In addition, the length range of the regenerate is limited by the length of the device, which makes it unable to reconstruct large mandibular defect especially those crossing the midline.
Extra-oral Bone Transport Devices
In our experience with this design, it proved to be simple, fast, with minimal interference with bone segments, wider range of distraction for angle-to-angle reconstruction. Yet, its disadvantages included poor control of the transport disc, pin-tract infection, pin extrusion, and retrusion of the newly formed bone in case of anterior reconstruction.